Methods for determining the location of objects in an outdoor environment with a clear view of the sky are well-known. Example methods can achieve a high degree of location accuracy using global navigation satellite systems (GNSS). Such a system may be implemented in a mobile device that processes a GNSS receiver configured to process signals received from multiple navigation satellites to determine its location based on trilateration using information encoded in the signals. GNSS systems, however, may not perform well in urban canyon environments due to multipath time delays resulting from satellite signals being reflected by buildings in the environment.
Locating an object in an indoor environment is typically more challenging as the signals from navigation satellites may not be able to be received in the indoor environment. Some indoor location systems use local radio sources, such as WiFi access points having known or fixed locations. Where the locations of the radio sources are known, the mobile device can determine its location with some degree of uncertainty using trilateration or by calculating a weighted centroid of the known locations of the RF sources each weighted by a value that depends on the strength of the signal received from the RF source. Where the locations of the radio sources are fixed, but possibly not known, the mobile device may determine its location using fingerprinting. This method correlates values of some feature of the received signals from multiple radio sources to a location on a floor-plan. The accuracy of indoor location systems suffers in venues including obstructions (such as people) that move and may distort the signals received by the mobile device.
Another method for determining location in an indoor venue employs pedestrian dead reckoning (PDR) sensors. These sensors, which may include, for example, accelerometers, gyroscopes, magnetometers and barometers, allow the mobile device to monitor changes in its location and, by combining these changes with a previously calculated location, to calculate a current location. Location systems based on PDR sensors tend to lose accuracy over longer terms of use due the inherent uncertainty of the sensors or due to sensor drift.